There is an increasing need in vehicles of all types for electronics which can supply data for use by the driver or some remote location away from the vehicle to determine in one example; in which direction the vehicle is traveling. This application is that of a stand-alone compass in which the heading of the vehicle could be displayed on a small electronic display as one of, let's say, eight points of the compass; North (N), South (S), East (E), West (W), Northeast (NE), Northwest (NW), Southeast (SE), and Southwest (SW). A more sophisticated version of such a stand-alone compass would be one which has sufficient performance and accuracy to display the heading degrees of a compass in 1 or 2 degree increments, as a numeric value or in an analog form like a needle on a compass rose.
Vehicle-mounted compasses must be calibrated to account for the magnetic signature of the vehicle. If there is a change in the magnetic signature of the vehicle a new calibration is necessary. However, it is often the case that the operator does not know the change and therefore, the reading will be off.
Also, in the event of transient magnetic disturbances, prior systems will hold the last heading before the disturbance began. When the disturbance ceases, a new correct heading is provided. Bridges, steel buildings or adjacent roadways built with ferrous material can cause transient magnetic anomalies.
One problem is in the detection of such an anomaly, because it may not be detected as an anomaly, in which case prior compasses will respond with incorrect readings. Also, an anomaly or recurring anomalies may be present for an extended length of time, for example, on modern highways such as overpasses, ramps and the like built with ferrous materials
In another example, Navigation systems of various types have been developed which assist the vehicle operator or a passenger to navigate to or away from a particular location. Navigation systems generally employ some form of triangulation of a source of three or more radio signals to determine the position or location of the vehicle. Such systems have been created using the technologies of LORAN, DECCA, GPS, FM and AM radios signals, and other RF radio systems. By plotting the position changes of the vehicle over time on an electronic map such a navigation system is created. Such navigation systems work reliably as long as the radio signals can be received without interruption. There are serious limitations to such systems because the loss of one or more of the radio signals due to signal blockage can serious reduce the accuracy of the navigation system and often result in the failure of the system.
Navigation and location determination systems such as, for example, those employing Global Positioning System (GPS) technology including Differential GPS (DGPS) technology, often have limitations caused by the temporary unavailability of the signals they are receiving and using to determine the position of the vehicle. In the GPS and DGPS example, there are times when there are insufficient satellite signals available, such as in areas around tall buildings or other obstructive masses, to maintain continuous measurement of the position of the vehicle.
Very similar requirements and similar limitations exist in another example, Vehicle Location as distinguished from Vehicle Navigation; that of enabling, in the vehicle or at some remote location, the determination of where the particular vehicle is in relationship to a map or any other form of vehicle location determination. Such, applications range from supplying vehicle location data to occupants of an automobile or any other land, sea, air or space vehicle to a vehicle location determination system in an automobile or any other land, sea, air or space vehicle which enables pinpointing the vehicle's location on some form of electronic map display or by producing coordinates within various coordinate systems which would enable the location of the vehicle on a non-electronic map or grid of some sort.
In such cases there is a need for something which can continue to compute the location of the vehicle during these times. That is to say aiding the navigation or location system by outputting a continuous series of vehicle positions and maintaining the ability of the system to continue to function during times of signal outage or blockage. Using the integration of sensor data from various sources, and processing those data to compute the change position of the vehicle over time can do this. Such a technique would process inputs of data such as speed and movement from a speed sensor or an accelerometer with the heading of the vehicle measured from that last known position of the vehicle before the signal outage or blockage. Such a system may be called a Flywheel and in the case of GPS systems, a GPS Flywheel because metaphorically the system continues to operate even as the primary navigation or location system has been degraded or lost.